The incidence of bloodstream infections caused by Candida species has increased dramatically, so that these organisms now account for 10% of all bloodstream isolates. During the process of hematogenous dissemination, it is likely that blood-borne organisms must adhere to and penetrate the endothelial lining of the vasculature to invade the tissue parenchyma. Thus, a potential method to prevent or treat hematogenously disseminated candidal infections is to augment the combined response of neutrophils and endothelial cells against this organism while it is within the intravascular compartment. We have shown that adding neutrophils to Candida-infected endothelium prevents endothelial cell injury in vitro. Also, we have found that Candida albicans by itself can stimulate endothelial cells to express leukocyte adhesion molecules and proinflammatory cytokines. The expression of these factors is greatly increased when neutrophils are added to endothelium infected with C. albicans. Together, these results suggest that there is a two-way exchange of signals between endothelial cells and neutrophils during their response to intravascular infection. The experiments outlined in this proposal are designed to elucidate the mechanisms that mediate this neutrophil amplification of the endothelial cell proinflammatory response to C. albicans. The influence of the microbial target (C. albicans) on the neutrophil enhancement of the endothelial cell response will be evaluated first. Based on these results, the immunomodulatory substances that mediate this neutrophil amplification will be identified. The expression of the leukocyte adhesion molecules, E-selectin and VCAM-1, will be used as a marker of endothelial cell activation in these experiments. Next, the activities of the immunomodulatory substances identified by the above experiments will be inhibited to determine if theses substances also influence the ability of neutrophils to kill C. albicans and protect endothelial cells from candidal injury. Finally, the results of these in vitro experiments will be evaluated in vivo. Both immunocompetent and neutropenic mice will be infected with C. albicans and immunohistochemistry will be used to detect the local expression of leukocyte adhesion molecules and cytokines at sites of candidal infection. Investigating the interactions between endothelial cells, neutrophils and C. albicans will enable us to determine the mechanism by which endothelial cells are activated in response to infection. The long-range goal of these studies is to devise endothelial cell-based strategies to enhance the host inflammatory response to blood-borne microbial pathogens.